This invention relates generally to injection molding of plastics and more particularly to an injection molded plastic component having a fuel vapor barrier layer and a method of making it.
Increasingly strict governmental regulations regarding the emission and escape to the atmosphere of hydrocarbon vapors are being continually promulgated. In various fuel systems, plastic fuel tanks are utilized because they are relatively inexpensive to produce, resistant to corrosion and lightweight. To reduce the escape to the atmosphere of hydrocarbon vapors from these fuel tanks a fuel vapor barrier layer is incorporated into the plastic fuel tank to inhibit and reduce the permeation of fuel vapors therethrough.
While the vapor barrier layer is generally effective at inhibiting fuel vapor permeation through the fuel tank walls themselves, various openings are formed through the fuel tanks to provide access to its interior. One hole preferably has a fill pipe attached thereto to permit fuel to be added to the fuel tank. One or more additional holes may be provided to receive a fuel pump, fuel vapor vent valve and other components desired to be disposed within the fuel tank. Closures for these openings have been formed from solely the structural material of the fuel tank, for example, high density polyethylene. Therefore, these closures provide less resistance to the permeation of hydrocarbon fuel vapors therethrough and undesirably increase the hydrocarbon emissions from the fuel tank. Providing a fuel vapor barrier layer on the closures is difficult and expensive because the materials typically used to form the barrier layer are not readily bondable or weldable to the structural material. Further, coextruding and thereafter molding a multiple layered polymeric article, as is typically done for multiple layer plastic fuel tanks, is difficult to control and relatively expensive.
An injection molded component having at least one structural layer of material and at least one fuel vapor barrier layer carried by the structural layer, and a method of making it utilizing separately formed structural and fuel vapor barrier layers. The vapor barrier layer may be trapped between two other interconnected layers, or may be bonded to a structural layer by an adhesive. In one form, an adhesive polymeric layer is separately injection molded. A fuel vapor barrier layer is then molded on one side of the adhesive layer and the adhesive layer is heated to activate the adhesive and bond it to the fuel vapor barrier layer. Thereafter, a structural layer of material, such as a layer of high density polyethylene (HDPE), is molded onto the other side of the adhesive layer and the adhesive layer is heated to activate the adhesive and bond the adhesive and structural layers together. In this manner, both the HDPE layer and the vapor barrier layer are bonded to the adhesive layer to provide a component having structural integrity due to the HDPE layer and a high resistance to the permeation of fuel vapor therethrough due to the fuel vapor barrier layer. Desirably, the heat generated during the steps of molding both the vapor barrier layer and the structural layer onto the adhesive layer is sufficient to activate the adhesive and bond the layers together.
In another form, material used to provide the structural integrity is blended with a material used as an adhesive for the component. This structural and adhesive material blend is injection molded into its desired shape. Thereafter, a layer of a suitable fuel vapor barrier material is molded onto the preformed structural and adhesive blend layer which is heated to activate the adhesive material within the blend layer to bond the vapor barrier layer to the blend layer. Thus, according to this aspect of the invention, the component has two layers of material providing for structural integrity of the component and the desired resistance to permeation of fuel vapor therethrough. Preferably, the heat from the molding of the vapor barrier layer onto the blend layer is sufficient to activate the adhesive and bond the layers together.
In accordance with yet another aspect of the present invention, an outer structural layer is injection molded to its desired final shape. A layer of fuel vapor barrier material is molded onto one side of the outer structural layer and an inner structural layer is molded over the fuel vapor barrier layer to encapsulate the fuel vapor barrier layer between the inner and outer structural layers. A mechanical lock such as undercut or dovetail grooves may be used to join the inner and outer structural layers together and to maintain the relative location and orientation of each of the layers. Thus, in this embodiment the component has three separate layers with a fuel vapor barrier layer sandwiched between two structural layers.
In another form, the component is comprised of an insert having a vapor barrier layer and a structural and/or adhesive material with a structural layer molded onto and bonded to the insert. The insert may be formed as a multiple layer extrusion or it may be molded.
Desirably, in each embodiment the injection molded component has at least one layer providing structural integrity for the component and at least one layer which reduces or inhibits the permeation of hydrocarbon fuel vapors through the component. Accordingly, such an injection molded component may be used as a closure for an opening through a fuel tank or to define a body of a component attached to the fuel tank such as for a fuel vapor vent valve, fill nipple weldment and the like. Desirably, the structural layers of the injection molded component facilitate direct attachment of the component to a plastic fuel tank, such as by ultrasonic or other welding methods. Further, the injection molded component could be connected and sealed to a metal fuel tank as well such as by metal fasteners and a gasket or an adhesive, for example.
Objects, features and advantages of this invention include providing injection molded components with a fuel vapor barrier layer to reduce permeation of hydrocarbons through the component which facilitates sealing engagement and attachment to another object such as a fuel tank, is weldable to typical plastic fuel tanks, permits individual layers of material to be separately molded, can be formed without an adhesive layer, is of relatively simple design and economical manufacture and assembly, is durable and has a long, useful life in service.